Re: [PATCH 1/2] dt-bindings: media: Add macros for video interface bus types

From: Rob Herring <robh@kernel.org>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>,
	devicetree@vger.kernel.org, linux-media@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Jacopo Mondi <jacopo@jmondi.org>,
	Eugen Hristev <eugen.hristev@microchip.com>,
	Hugues Fruchet <hugues.fruchet@foss.st.com>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Alexandre Torgue <alexandre.torgue@foss.st.com>
Subject: Re: [PATCH 1/2] dt-bindings: media: Add macros for video interface bus types
Date: Tue, 1 Mar 2022 09:04:10 -0600	[thread overview]
Message-ID: <Yh416qrZr32PzMtJ@robh.at.kernel.org> (raw)
In-Reply-To: <YhvqLL0LYWt2ryaE@pendragon.ideasonboard.com>

On Sun, Feb 27, 2022 at 11:16:28PM +0200, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Sun, Feb 27, 2022 at 11:07:23PM +0200, Sakari Ailus wrote:
> > On Sun, Feb 27, 2022 at 10:33:51PM +0200, Laurent Pinchart wrote:
> > > Add a new dt-bindings/media/video-interfaces.h header that defines
> > > macros corresponding to the bus types from media/video-interfaces.yaml.
> > > This allows avoiding hardcoded constants in device tree sources.
> > > 
> > > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > ---
> > >  include/dt-bindings/media/video-interfaces.h | 16 ++++++++++++++++
> > >  1 file changed, 16 insertions(+)
> > >  create mode 100644 include/dt-bindings/media/video-interfaces.h
> > > 
> > > diff --git a/include/dt-bindings/media/video-interfaces.h b/include/dt-bindings/media/video-interfaces.h
> > > new file mode 100644
> > > index 000000000000..e38058e1cca7
> > > --- /dev/null
> > > +++ b/include/dt-bindings/media/video-interfaces.h
> > > @@ -0,0 +1,16 @@
> > > +/* SPDX-License-Identifier: GPL-2.0-only */
> > > +/*
> > > + * Copyright (C) 2022 Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > + */
> > > +
> > > +#ifndef __DT_BINDINGS_MEDIA_VIDEO_INTERFACES_H__
> > > +#define __DT_BINDINGS_MEDIA_VIDEO_INTERFACES_H__
> > > +
> > > +#define MEDIA_BUS_TYPE_CSI2_CPHY		1
> > > +#define MEDIA_BUS_TYPE_CSI1			2
> > > +#define MEDIA_BUS_TYPE_CCP2			3
> > > +#define MEDIA_BUS_TYPE_CSI2_DPHY		4
> > > +#define MEDIA_BUS_TYPE_PARALLEL			5
> > 
> > I've been long thinkin of renaming "PARALLEL" as "BT.601" which it really
> > is. I don't mind postponing that, but I think you could as well start here.
> > Up to you.
> 
> I think it's a good idea, but we then need to decide what to do with
> other types of parallel buses. Let's start this discussion now, and
> implement it in a patch on top of this series.

5 and what it means is an ABI. If it is ambiguous and needs to be more 
specific, then you need new numbers for all of those specific types.

If it is just a rename, I prefer it is done from the start.

> > Should this be somehow visible in video-interfaces.yaml?
> 
> I wish we could use macros in .yaml files instead of numerical values,
> but I don't think that's possible. I can do this:
> 
>    bus-type:
>      $ref: /schemas/types.yaml#/definitions/uint32
>      enum:
> -      - 1 # MIPI CSI-2 C-PHY
> -      - 2 # MIPI CSI1
> -      - 3 # CCP2
> -      - 4 # MIPI CSI-2 D-PHY
> -      - 5 # Parallel
> -      - 6 # BT.656
> +      - 1 # MIPI CSI-2 C-PHY (MEDIA_BUS_TYPE_CSI2_CPHY)
> +      - 2 # MIPI CSI1 (MEDIA_BUS_TYPE_CSI1)
> +      - 3 # CCP2 (MEDIA_BUS_TYPE_CCP2)
> +      - 4 # MIPI CSI-2 D-PHY (MEDIA_BUS_TYPE_CSI2_DPHY)
> +      - 5 # Parallel (MEDIA_BUS_TYPE_PARALLEL)
> +      - 6 # BT.656 (MEDIA_BUS_TYPE_BT656)

Seems a bit redundant to have both comment text and define. The only 
part missing from the defines is 'MIPI'.

>      description:
> -      Data bus type.
> +      Data bus type. Use the macros listed above (defined in
> +      dt-bindings/video-interfaces.h) instead of numerical values.
> 
> Any better proposal ?
> 
> > > +#define MEDIA_BUS_TYPE_BT656			6
> > > +
> > > +#endif /* __DT_BINDINGS_MEDIA_VIDEO_INTERFACES_H__ */
> 
> -- 
> Regards,
> 
> Laurent Pinchart
> 